Insulting or attacking other users, even so much saying "fuck you", "fuck [this group of people]", "you're an idiot" or anything like that while debating IS against the rules of Lemmy.ml. This goes for every political view, you DO NOT get free passes no matter if you're leftist, rightist, communist, anarchist, liberal, etc. If you're confident of your position you should be able to debate in a civil manner without cursing someone else out. I understand that debates can get heated and frustrating, hell I've debated with a good bunch of users, but you can still express that without resorting to name calling or insults.
Check the modlog, we HAVE removed replies of this nature from every political view, and even if we don't say it every time, we DO keep track of both removals per user and general behaviour even if it doesn't get removed, and too many infractions WILL result in a ban.
That said, it is NOT against the rules to present countering facts or opinions, or to have political opinions in general. Don't report comments for "being pro communist" or "being pro China" unless they have broken an actual rule, namely the ones about being civil. Don't attack or insult people from Lemmygrad just because they're from Lemmygrad or they're arguing for Marxism-Leninism or supporting a country you don't. If they're presenting their points in a civil manner (which had been the case for almost everyone from Lemmygrad), you can either read it and respond in kind with your questions or counterpoints, or just move on. People coming over from other instances is not brigading if they're mostly being civil, that's the whole point of federation.
Things people disagree with getting down voted is also acceptable, it's not considered an attack on you if your comment has a negative score, and it doesn't even significantly affect the ranking because of the relatively low comment volumes currently on Lemmy. It's just imaginary internet points, relax.